1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a mobile communication system in which traffics are equalized between switching apparatuses.
2. Description of the Related Art
Conventionally, various mobile telephone systems are known such as a PHS (personal handy phone system) in which a minimal cell method is adopted, an automobile telephone system in which a small cell method is used, and a PDS (portable digital phone system). Each of the mobile phone systems have a merit and a defect.
For example, in the PHS system, the area which a radio wave reaches has the radius about 100 m from a base station. Therefore, in order to form a wide service area, a lot of base stations are densely installed. As a result, there is a problem in that there is an area where the radio wave is difficult to be received, depending on the installed state of the base stations. On the other hand, there is an advantage in low communication charge in the PHS system, compared with the other mobile phone systems.
On the other hand, in the PDS system, because the small cell method is adopted such that the radio wave can reach to a relatively wide area, there is a low possibility of the above-mentioned problem that the radio wave is difficult to be received. However, there is a problem in a high communication charge in the PDS system, compared with the PHS system.
In order to eliminate such a conventional problem, a dual band portable phone is discussed in recent years to be possible to be applied to two mobile phone systems such as the PHS system and the PDS system. In the following description, an operation mode is referred to as a xe2x80x9cPHS modexe2x80x9d when the dual band portable phone operates as a mobile station of the PHS system, and as a xe2x80x9cPDS modexe2x80x9d when the dual band portable phone operates as the mobile station of the PDS system.
The switching of the operation mode in the dual band portable phone, i.e., the switching of the mobile communication system is conventionally carried out on the dual band portable phone. That is, a control unit of the dual band portable phone operates in the PHS mode when the dual band portable phone is in a service area of the PHS system and out of any service area of the PDS system. Oppositely, the operation mode of the dual band portable phone operates is automatically switched to the PDS mode when the dual band portable phone is out of any service area of the PHS system and in a service area of the PDS system. Also, the control unit of the dual band portable phone automatically switches the operation mode to be PHS mode with low communication charge, when the dual band portable phone is in an area which is covered by the PHS system and the PDS system.
Also, the dual band portable phone is possible to operate in either of the PHS mode or the PDS mode in response to the operation of a predetermined button by a user in addition to the automatic switching.
Conventionally, the mobile communication system to which the dual band portable phone belongs is selectively switched based on the control of the dual band portable phone itself, as mentioned above. In this case, the traffic of a base station of each mobile telephone system is not considered. Therefore, the dual band portable phone sometimes operates in the PHS mode with a large traffic quantity while the traffic of the PDS system is small. Or, the opposite situation occurs. As a result, there is a problem in degradation of communication quality due to traffic jam.
It should be noted that xe2x80x9ca digital radio communication system and a digital radio communication apparatusxe2x80x9d is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-65606) as the technique to improve the communication quality. In the reference, the communication system is composed of base stations A1 to C1 and terminal stations A2 to C2. Radio communications between the base station and the terminal station and between the base stations are carried out. In such a digital radio communication system, the base station selects a combination of the frequency with a smallest transmission error to noise around the base station and a convolution code, and communicates using the frequency and the convolution code of the selected combination.
In this way, an error correcting code used for the communication is appropriately selected in accordance with the radio wave situation around the communication environment. As a result, the deterioration of the communication quality which is caused by the transmission path error can be restrained because the transmission path error becomes little. However, in this digital radio communication system, it is not possible to prevent the deterioration of the communication quality which is caused by the large traffic.
In conjunction with the above description, a mobile communication system is described in Japanese Laid Open Patent Application (JP-A-Heisei 4-70094). In this reference, a service area is composed of a plurality of zones, in which base stations are respectively provided. A mobile station communicates with one of the base stations. When the mobile station moves to an adjacent area during the communication, the base station is switched to another base station for the adjacent area. Each base station has notifying means for notifying a control channel frequency information. of the other base station for the adjacent area and a channel operation percentage of the base station. The mobile station has monitoring means and a selecting means. The monitoring means monitors the channel operation percentage notified from each base station and reception levels from each base station. The selecting means selects one of the base stations which has the reception level higher than a predetermined value and the channel operation percentage lower than a predetermined value as a switching destination base station.
Also, a traffic distributing system in a mobile communication system is described in Japanese Laid Open Patent Application (JP-A-Heisei 5-75530). In the reference, a traffic distribution start threshold value T1, a traffic distribution stop threshold value T2, and a channel selection re-execution instruction transmission period xcfx84 are stored in a main control unit of a radio base station. When a communication channel usage percentage exceeds the traffic distribution start threshold value T1, the transmission of a channel selection re-execution instruction is started at the transmission period Txcfx84. When the communication channel usage percentage is decreased below the traffic distribution stop threshold value T2, the transmission of the channel selection re-execution instruction is stopped. Thus, a mobile terminal communicating with a radio base station which has no empty communication channel because of a high traffic quantity is made to communicate with another radio base station.
Also, a mobile communication system is described in Japanese Laid Open Patent Application (JP-A-Heisei 7-226973). In the reference, permission or inhibition of mode switching between one mode and another mode is set for each of zones which corresponds to at least one mode. An unnecessary mode switching is restrained in the mobile communication system in which communication is carried out using one selected from a plurality of modes.
Also, a communication channel switching system is described in Japanese Laid Open Patent Application (JP-A-Heisei 8-70479). In the reference, a control station (5) notifies a usable communication channel to a mobile station (1) via base station (2, 3). The mobile station monitors the present communication condition. When the communication condition is degraded, the mobile station independently switches to a new channel by which good communication condition is attained. The mobile station notifies the new channel to the control station (5) via the base station (2, 3).
Also, a communication restriction control system is described in Japanese Laid Open Patent Application (JP-A-Heisei 9-9340). In the reference, threshold values axe2x80x2 and bxe2x80x2 are predetermined based on a use percentage of a communication channel and stored in a communication restriction control section (33). The communication restriction control section inputs a traffic quantity of a communication channel from a call control section (32) and calculates the use percentage. When the calculated use percentage exceeds the threshold value axe2x80x2, a notice a is sent out to carry out restriction to roaming subscribers such as call origination restriction. When the calculated use percentage exceeds the threshold value bxe2x80x2, a notice b is sent out to carry out restriction to all subscribers such as call origination restriction.
Also, a method of implementing soft hand-off in a radio communication system is described in Japanese Laid Open Patent Application (JP-A-Heisei 10-145834). In the reference, a communication channel is provided between adjacent base stations to be logically separated from a mobile switching station. Traffic information is exchanged between the base stations via the communication channel. Thus, the soft hand-off by the base station can be realized.
Therefore, an object of the present invention is to provide a mobile communication system in which traffics are equalized between switching apparatus so that the communication quality can be improved.
In order to achieve an aspect of the present invention, a mobile communication system includes first and second switching apparatuses, an information channel provided between the first and second switching apparatuses, a plurality of base stations managed by each of the first and second switching apparatuses, and a mobile station. The mobile station can communicate with the first switching apparatus through one of the plurality of base stations managed by the first switching apparatus and with the second switching apparatus through one of the plurality of base stations managed by the second switching apparatus. The first and second switching apparatuses detect traffics therethrough as first and second traffics, respectively, and the second switching apparatus notifies the second traffic to the first switching apparatus via the information channel. The first switching apparatus controls the mobile station and the second switching apparatus based on the first and second traffics such that the mobile station which is currently communicating with the first switching apparatus communicates with the second switching apparatus.
The first switching apparatus may control the mobile station and the second switching apparatus based on the first and second traffics and first and second threshold values. In this case, the first switching apparatus compares the first traffic and the first threshold value, and the second traffic and the second threshold value. Then, the first switching apparatus controls the mobile station and the second switching apparatus when the first traffic is equal to or larger than the first threshold value and when the second traffic is smaller than the second threshold value. Also, the first switching apparatus continues the communication with the mobile station when the first traffic is smaller than the first threshold value or when the second traffic is larger than the second threshold value.
In the above, the first and second switching apparatuses may operate under a same communication system. Instead, the first and second switching apparatuses may operate under different communication systems from each other. In this case, it is preferable that the first and second switching apparatuses operate under two of a PHS communication system, a PDS communication system, and an automobile communication system.
The first switching apparatus may issue a switching request to the mobile station via the base station and to the second switching apparatus via the information channel, when the mobile station should communicate with the second switching apparatus. When a switching confirmation is received from the mobile station and the second switching apparatus, the first switching apparatus stops the communication with the mobile station.
In order to achieve another aspect of the present invention, a switching apparatus includes a traffic detecting unit and a traffic detecting unit. The traffic detecting unit detects a traffic through the switching apparatus and transmits the detected traffic to other switching apparatuses. The control unit issues a switching request to one of the other switching apparatuses and a mobile station communicating with the switching apparatus based on the detected traffic and a traffic received from the one switching apparatus. The control unit stops the communication with the mobile station when a switching confirmation is received from the mobile station and the one switching apparatus.
The control unit issues the switching request to the one switching apparatus and the mobile station based on the detected traffic and the received traffic and first and second threshold values such that the mobile station which is currently communicating with the switching apparatus communicates with the one switching apparatus. The first and second threshold values are allocated to the switching apparatus and the one switching apparatus. In this case, the control unit compares the first traffic and the first threshold value, and the second traffic and the second threshold value. Then, the control unit issues the switching request to the mobile station and the one switching apparatus when the first traffic is equal to or larger than the first threshold value and when the second traffic is smaller than the second threshold value. In this case, the switching apparatus continues the communication with the mobile station when the first traffic is smaller than the first threshold value or when the second traffic is larger than the second threshold value.
In order to achieve still another aspect of the present invention, a mobile terminal includes first and second communication radio sections corresponding to first and second communication systems, respectively, and a control unit. The control unit issues a switching confirmation via the first communication radio section when a switching request is received through the first communication radio section, and then starts a communication through the second communication radio section.
In order to achieve yet still another aspect of the present invention, a method of averaging traffics between a plurality of switching apparatuses, includes:
detecting traffics as first and second traffics by first and second switching apparatuses of the plurality of switching apparatuses, respectively;
notifying the second traffic from the second switching apparatus to the first switching apparatus;
issuing a switching request to the second switching apparatus and a mobile station currently communicating with the first switching apparatus, based on the first and second traffics;
stopping the communication with the mobile station in response to a switching confirmation from the mobile station and a switching confirmation from the second switching apparatus such that communication is carried out between the second switching apparatus and the mobile station.
The switching request may be issued to the second switching apparatus and the mobile station based on the first and second traffics and first and second threshold values. In this case, for the issuing the switching request, the first traffic and the first threshold value and the second traffic and the second threshold value are compared. The switching request is issued to the second switching apparatus and the mobile station based on the first and second traffics and first and second threshold values, when the first traffic is equal to or larger than the first threshold value and when the second traffic is smaller than the second threshold value. The issue of the switching request is stopped when the first traffic is smaller than the first threshold value or when the second traffic is larger than the second threshold value.
Also, the first and second switching apparatuses may operate under a same communication system. Instead, the first and second switching apparatuses may operate under different communication systems from each other. In this case, it is preferable that the first and second switching apparatuses operate under two of a PHS communication system, a PDS communication system, and an automobile communication system.